Roots-type fluid machine

ABSTRACT

A roots-type fluid machine including a set of rotors and a rotor housing is disclosed. The rotor housing accommodates the rotors and has a suction space. The set of rotors mesh with each other and rotate in the rotor housing so that fluid is drawn into the suction space and discharged from the rotor housing. Each of the set of rotors includes a tooth having a twisted portion and a different shape variation portion. The twisted portion has a twist angle that changes linearly or non-linearly about a rotation axis of the corresponding rotor with respect to the variation of the position in the direction of the axis. The different shape variation portion has a twisted angle that changes by a smaller degree than the variation of the twist angle of the twisted portion.

BACKGROUND OF THE INVENTION

The present invention relates to a roots-type fluid machine in which a set of rotors mesh with each other and rotate in a rotor housing so that fluid is drawn into a suction space in the rotor housing and discharged from the rotor housing.

A roots-type fluid machine with rotors having helical teeth is disclosed in, for example, Japanese Laid-Open Patent Publication No. 2-227588. The teeth of the rotors are monotonically twisted into helical form around the rotation axes of the rotors. In the roots-type fluid machine that uses helical rotors, the rotors are helically twisted from one end to the other end. When the following equation (1), in which the twist angle of the rotors is expressed by Φ, is satisfied, the volumetric change (the suction amount of fluid to a suction space per unit time) does not fluctuate in the suction space, which is located between the pair of meshed rotors and communicates with an inlet formed in the rotor housing.

Φ=(360°/2n)×X   (1)

in which n is the number of the teeth of the rotors (number of lobes), and X is a positive integer. In a structure where the volumetric change in the suction space does not fluctuate, the suction pulsation basically does not occur.

However, in the roots-type fluid machine, which is operated without providing oil between the rotor housing and the rotors and between the rotors for lubrication, since a clearance is provided for avoiding sliding contact between the rotor housing and the rotors and between the rotors, fluid leaks between the rotor housing and the rotors and between the rotors. Thus, although the volumetric change of the suction space does not fluctuate, the suction pulsation does not become zero, and the suction pulsation of fundamental order caused by fluid leakage remains. For example, if the rotors each have a three-lobe transverse cross section as disclosed in Japanese Laid-Open Patent Publication No. 2-227588, the suction pulsation of the fundamental order of sixth order remains.

FIGS. 17A and 17B show a roots-type fluid machine with three-lobe rotors 37, 38. The roots-type fluid machine includes an inlet J1 and a suction space S, which communicates with the inlet J1. The roots-type fluid machine further includes a discharge space P and an outlet J2, which communicates with the discharge space P. FIG. 17A shows a state where the distal end portion of a tooth 371 of the rotor 37 is fitted in a tooth bottom portion 382 of the rotor 38. FIG. 17B shows a state where the rotors 37, 38 are rotated by 30° from the state in FIG. 17A, and where the side portion of the tooth 371 of the rotor 37 has come close to the side portion of the tooth 381 of the rotor 38.

The size of a minimum clearance CL1 at a closest portion K1 shown in FIG. 17A is equal to the size of a minimum clearance CL2 at a closest portion K2 shown in FIG. 17B. The clearance increases as the distance from the minimum clearance CL1 increases along circumferential direction of the distal end portion of the tooth 371 of the rotor 37. The clearance increases as the distance from the minimum clearance CL2 increases along the circumferential direction of the side portion of the tooth 371 of the rotor 37.

However, the change in the size of the clearance of the closest portion K1 shown in FIG. 17A (the change along the circumferential direction of the distal end portion of the tooth 371 of the rotor 37) is smaller than the change in the size of the clearance at the closest portion K2 shown in FIG. 17B (the change along the circumferential direction of the side portion of the tooth 371 of the rotor 37). Thus, the fluid leakage between the rotors 37, 38 in the state shown in FIG. 17A (fluid leakage to the suction space S from the discharge space P via the space between the rotors 37, 38) is small, and the fluid leakage between the rotors 37, 38 in the state shown in FIG. 17B is great.

The state similar to that shown in FIG. 17A occurs six times while the rotors 37, 38 rotate once, and the state similar to that shown in FIG. 17B occurs six times while the rotors 37, 38 rotate once. Thus, in the roots-type fluid machine, which uses three-lobe helical rotors 37, 38, the suction pulsation of the fundamental order of sixth order is generated due to fluid leakage.

If the transverse cross-sectional view of the rotors is two-lobe in shape, the suction pulsation of the fundamental order of fourth order caused by fluid leakage remains.

SUMMARY OF THE INVENTION

Accordingly, it is an objective of the present invention to reduce suction pulsation caused by fluid leakage in a roots-type fluid machine that uses rotors including twisted portions. The twist angle of each twisted portion about the rotation axis of the associated rotor changes linearly or nonlinearly with respect to changes in the position in the axial direction of the rotation axis of the rotor.

To achieve the above objective, and in accordance with one aspect of the present invention, a roots-type fluid machine including a set of rotors and a rotor housing is provided. The rotor housing accommodates the rotors and has a suction space. The set of rotors mesh with each other and rotate in the rotor housing so that fluid is drawn into the suction space and discharged from the rotor housing. Each of the set of rotors includes a tooth having a twisted portion and a different shape variation portion. The twisted portion has a twist angle that changes linearly or non-linearly about a rotation axis of the corresponding rotor with respect to the variation of the position in the direction of the axis. The different shape variation portion has a twisted angle that changes by a smaller degree than the variation of the twist angle of the twisted portion.

Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which:

FIG. 1A is a plane cross-sectional view illustrating a fluid machine according to a first embodiment of the present invention;

FIG. 1B is a side view illustrating one of the rotors;

FIG. 1C is a side view illustrating one of the rotors;

FIG. 2A is a cross-sectional view taken along line 2A-2A in FIG. 1A;

FIG. 2B is a cross-sectional view taken along line 2B-2B in FIG. 2A;

FIG. 3A is a graph showing a variation in a twist angle;

FIG. 3B is a graph showing suction pulsation;

FIG. 3C is a graph showing antiphase pulsation;

FIG. 4A is a side view illustrating a rotor according to a second embodiment;

FIG. 4B is a side view illustrating a rotor according to the second embodiment;

FIG. 5 is a graph showing a variation in a twist angle;

FIG. 6A is a side cross-sectional view illustrating a rotor according to a third embodiment;

FIG. 6B is a side cross-sectional view illustrating a rotor according to the third embodiment;

FIG. 7 is a cross-sectional view illustrating the rotors according to the third embodiment;

FIG. 8A is a side view illustrating a rotor according to a fourth embodiment;

FIG. 8B is a side view illustrating a rotor according to the fourth embodiment;

FIG. 9 is a graph showing a variation in a twist angle;

FIG. 10A is a side view illustrating a rotor according to a fifth embodiment;

FIG. 10B is a side view illustrating a rotor according to the fifth embodiment;

FIG. 11A is a graph showing a variation in twist angle;

FIG. 11B is a graph showing suction pulsation;

FIG. 11C is a graph showing antiphase pulsation;

FIG. 12A is a cross-sectional view illustrating rotors according to a sixth embodiment;

FIG. 12B is a side view illustrating one of the rotors;

FIG. 12C is a side view illustrating one of the rotors;

FIG. 13A is a graph showing a variation in a twist angle;

FIG. 13B is a graph showing the suction pulsation;

FIG. 13C is a graph showing antiphase pulsation;

FIG. 14 is a graph showing a modified embodiment;

FIG. 15 is a graph showing a modified embodiment;

FIG. 16 is a graph showing a modified embodiment;

FIG. 17A is a schematic diagram for explaining suction pulsation caused by fluid leakage; and

FIG. 17B is a schematic diagram for explaining suction pulsation caused by fluid leakage.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A first embodiment of the present invention will now be described with reference to FIGS. 1A to 3C.

As shown in FIG. 1A, a partition wall 12 is coupled to the rear end of a front housing member 11, and an electric motor M is coupled to the partition wall 12 with a gear housing member 13. The front housing member 11, the partition wall 12, the gear housing member 13, and a housing member M1 of the electric motor M configure a housing assembly of a roots-type fluid machine 10.

The front housing member 11 and the partition wall 12 configure a rotor housing 23, which forms a pump chamber 231. A shaft hole 121 extends through the partition wall 12, and a shaft hole 141 is formed in an end wall 14 of the front housing member 11. The end wall 14 of the front housing member 11 and the partition wall 12 rotatably support a rotary shaft 15 of the electric motor M with radial bearings 16, 17 fitted in the shaft holes 121, 141. Similarly, a shaft hole 122 extends through the partition wall 12, and a shaft hole 142 is formed in the end wall 14 of the front housing member 11. A rotary shaft 18 is inserted in the shaft holes 122, 142. The end wall 14 of the front housing member 11 and the partition wall 12 rotatably support the rotary shaft 18 with radial bearings 19, 20 fitted in the shaft holes 122, 142. The rotary shafts 15, 18 are arranged in parallel to each other. Lip seal type shaft seals 29, 30 are provided.

As shown in FIG. 2B, a rotor 21 is secured to the rotary shaft 15, and a rotor 22 is secured to the rotary shaft 18. The rotors 21, 22 are accommodated in the pump chamber 231 in a state where the rotors 21, 22 mesh with each other with a slight gap kept in between.

The rotor 21 has three teeth 24, which protrude in the radial direction of the rotary shaft 15. The rotor 22 has three teeth 25, which protrude in the radial direction of the rotary shaft 15. The three teeth 24 of the rotor 21 are arranged at equal angular intervals of 120° about a rotation axis 151 of the rotary shaft 15, and the rotor 21 has rotational symmetry of 120° about the rotation axis 151. Similarly, the three teeth 25 of the rotor 22 are arranged at equal angular intervals of 120° about a rotation axis 181 of the rotary shaft 18, and the rotor 22 has rotational symmetry of 120° about the rotation axis 181.

As shown in FIG. 1B, each tooth 24 includes a first twisted portion 241, which is helically twisted clockwise about the rotation axis of the rotor 21 (that is, the rotation axis 151 of the rotary shaft 15), and a second twisted portion 242, which is helically twisted clockwise about the rotation axis 151. Furthermore, each tooth 24 includes a non-twisted portion 240, which is located between the first twisted portion 241 and the second twisted portion 242. The twist angle of the first twisted portion 241 and the second twisted portion 242 changes linearly along the axial direction of the rotation axis 151. The non-twisted portion 240 is a straight line, which is parallel to the rotation axis 151. That is, the non-twisted portion 240 does not twist along the axial direction of the rotation axis 151.

As shown in FIGS. 1C and 2A, each tooth 25 includes a first twisted portion 251, which is helically twisted counterclockwise about the rotation axis of the rotor 22 (that is, the rotation axis 181 of the rotary shaft 18), and a second twisted portion 252, which is helically twisted counterclockwise about the rotation axis 181. Furthermore, each tooth 25 includes a non-twisted portion 250, which is located between the first twisted portion 251 and the second twisted portion 252. The twist angle of the first twisted portion 251 and the second twisted portion 252 changes linearly along the axial direction of the rotation axis 181. The non-twisted portion 250 is a straight line, which is parallel to the rotation axis 181. That is, the non-twisted portion 250 does not twist along the axial direction of the rotation axis 181.

The length of the first twisted portion 241 in the direction of the rotation axis 151 is equal to the length of the first twisted portion 251 in the direction of the rotation axis 181. The length of the second twisted portion 242 in the direction of the rotation axis 151 is equal to the length of the second twisted portion 252 in the direction of the rotation axis 181. The length of the non-twisted portion 240 in the direction of the rotation axis 151 and the length of the non-twisted portion 250 in the direction of the rotation axis 181 are the same length L (shown in FIGS. 1B, 1C, and 3A). The length L of the non-twisted portions 240, 250 is shorter than the length of the first twisted portions 241, 251 and the length of the second twisted portions 242, 252. The first twisted portion 241 of the rotor 21 meshes with the first twisted portion 251 of the rotor 22, and the second twisted portion 242 of the rotor 21 meshes with the second twisted portion 252 of the rotor 22. The non-twisted portion 240 of the rotor 21 meshes with the non-twisted portion 250 of the rotor 22.

As shown in FIG. 1A, the rotary shaft 18 extends through the partition wall 12 and protrudes inside the gear housing member 13. Gears 26, 27 are fastened to parts of the rotary shafts 15, 18 located in the gear housing member 13 in a state where the gears 26, 27 mesh with each other. When the electric motor M is driven, the rotary shaft 15 is rotated in the direction of arrow R1, and the rotor 21 is rotated integrally with the rotary shaft 15 in the direction of arrow R1. The rotary shaft 18 receives driving power from the electric motor M via the gears 26, 27. The rotary shaft 18 is rotated in the opposite direction from the rotary shaft 15 as shown by arrow R2, and the rotor 22 is rotated integrally with the rotary shaft 18 in the direction of arrow R2.

As shown in FIG. 2B, an inlet 281 and an outlet 282 are formed in a circumferential wall 28 of the front housing member 11 to be connected to the pump chamber 231. The rotors 21, 22 define a suction space S, which communicates with the inlet 281, in the pump chamber 231. When the electric motor M is operated, the rotary shaft 15 is rotated in the direction of arrow R1, and the rotary shaft 18 is rotated in the direction of arrow R2, and the rotors 21, 22 are rotated integrally with the rotary shafts 15, 18. As the rotors 21, 22 are rotated, fluid (air in the first embodiment) is drawn into the suction space S from the inlet 281. The air that is drawn into the suction space S is transferred to the outlet 282, and the air that is transferred to the outlet 282 is discharged from the outlet 282.

In the first embodiment, the air that is discharged from the outlet 282 is supplied to a fuel cell (not shown). A restrictor is located in a passage (not shown) downstream of the fuel cell, and the air discharged from the outlet 282 is supplied to the fuel cell as compressed air.

A variation line E1 in the graph of FIG. 3A shows the relationship between the position H in the axial direction of the rotation axis 151 and the twist angle Φ regarding parts of the rotor 21 where the lengths of the radial lines, which extend from the rotation axis 151 of the rotor 21 to the circumferential surfaces of the teeth 24, are equal (for example, the vertexes of the teeth 24 of the rotor 21). The position of an end surface 211 of the rotor 21 is represented by the position H=0, the position of an end surface 212 of the rotor 21 is represented by the position H=He. The twist angle corresponding to the position of the end surface 211 is represented by the twist angle Φ=0°, and the twist angle corresponding to the position of the end surface 212 is represented by the twist angle Φ=Φe. A straight segment E11 of the variation line E1 represents a variation in the twist angle of the first twisted portion 241, and a straight segment E12 of the variation line E1 represents a variation in the twist angle of the second twisted portion 242. A straight segment E10 of the variation line E1 represents a variation in the twist angle of the non-twisted portion 240.

The first twisted portion 241 and the second twisted portion 242 are twisted portions where the twist angle Φ about the rotation axis 151 monotonically (in this case, linearly) changes with respect to the change in the position H in the axial direction of the rotation axis 151. The twist angle variation of the first twisted portion 241 is equal to the twist angle variation of the second twisted portion 242. The non-twisted portion 240 is a different shape variation portion having a twist angle, which varies by a smaller degree compared to the twist angle variations of the first twisted portion 241 and the second twisted portion 242.

A variation line E2 in the graph of FIG. 3A represents the relationship between the twist angle Φ and the position H in the axial direction of the rotation axis 181 regarding parts of the rotor 22 where the lengths of the radial lines, which extend from the rotation axis 181 of the rotor 22 to the circumferential surfaces of the teeth 25, are equal (for example, the vertexes of the teeth 25 of the rotor 22). The position of an end surface 221 of the rotor 22 is represented by the position H=0, the position of an end surface 222 of the rotor 22 is represented by the position H=He. The twist angle corresponding to the position of the end surface 221 is represented by the twist angle Φ=0°, and the twist angle corresponding to the position of the end surface 222 is represented by the twist angle Φ=−Φe. A straight segment E21 of the variation line E2 represents a variation in the twist angle of the first twisted portion 251, and a straight segment E22 of the variation line E2 represents a variation in the twist angle of the second twisted portion 252. A straight segment E20 of the variation line E2 represents a variation in the twist angle of the non-twisted portion 250.

The first twisted portion 251 and the second twisted portion 252 are twisted portions where the twist angle Φ about the rotation axis 181 monotonically (in this case, linearly) changes with respect to the change in the position H in the axial direction of the rotation axis 181. The twist angle variation of the first twisted portion 251 is equal to the twist angle variation of the second twisted portion 252. The non-twisted portion 250 is a different shape variation portion having a variation in a twist angle that is smaller than the twist angle variations of the first twisted portion 251 and the second twisted portion 252.

In the first embodiment, Φe=60°, and −Φe=−60°. Also, the straight segment E10 is at a position of Φ=30°, and the straight segment E20 is at a position of Φ=−30°. That is, the length of the first twisted portion 241 of the rotor 21 in the direction of the rotation axis 151 is equal to that of the second twisted portion 242. Furthermore, the non-twisted portion 240 is located between the position corresponding to the twist angle Φ=30° of first twisted portion 241 and the position corresponding to the twist angle Φ=30° of the second twisted portion 242. The non-twisted portion 240 is located at a position overlapping the center of the rotor 21 in the direction of the rotation axis 151. Similarly, the length of the first twisted portion 251 of the rotor 22 in the direction of the rotation axis 181 is equal to that of the second twisted portion 252. Furthermore, the non-twisted portion 250 is located between the position corresponding to the twist angle Φ=−30° of the first twisted portion 251 and the position corresponding to the twist angle Φ=−30° of the second twisted portion 252. The non-twisted portion 250 is located at a position overlapping the center of the rotor 22 in the direction of the rotation axis 181.

A waveform G1 in FIG. 3C represents the pulsation generated by fluctuation of the volumetric change in the suction space S. The volumetric change in the suction space S refers to the amount of change in the volume of the suction space S per unit time (suction amount of fluid to the suction space S per unit time). The rotational angle θ=0° represents the rotation position of the rotors 21, 22 in the state shown in FIG. 2B. In the case of conventional helical rotors, which do not have the non-twisted portions 240, 250 and are formed by only the first twisted portions 241, 251 and the second twisted portions 242, 252, the volumetric change in the suction space is constant. However, in the case of the rotors 21, 22, the volumetric change in the suction space S fluctuates due to the existence of the non-twisted portions 240, 250. Valleys of the pulsation shown by the waveform G1 are in the vicinity of the rotational angle θ=30°×(2n−1) since the non-twisted portion 240 is located between the position corresponding to the twist angle Φ=30° of the first twisted portion 241 and the position corresponding to the twist angle Φ=30° of the second twisted portion 242, and the non-twisted portion 250 is located between the position corresponding to the twist angle Φ=−30° of the first twisted portion 251 and the position corresponding to the twist angle Φ=−30° of the second twisted portion 252. Here, n is an integer greater than or equal to one. Hereinafter, the pulsation shown by the waveform G1 is referred to as an antiphase pulsation G1.

A waveform Fo6 shown in FIG. 3B shows one example of the suction pulsation caused by fluid leakage in a case where rotors without the non-twisted portions 240, 250 are used. Hereinafter, the suction pulsation shown by the waveform Fo6 is referred to as a suction pulsation Fo6 caused by fluid leakage. In the case of the roots pump that uses the rotors with three teeth, the fundamental order of the suction pulsation caused by fluid leakage is sixth order. The peaks of the suction pulsation Fo6 caused by fluid leakage are in the vicinity of the rotational angle θ=30°×(2n−1), and the valleys of the suction pulsation Fo6 caused by fluid leakage are in the vicinity of the rotational angle θ=30°×2n. Here, n is an integer greater than or equal to one.

A waveform F1 in FIG. 3B shows one example of suction pulsation when the rotors 21, 22 including the non-twisted portions 240, 250 are used. The suction pulsation shown by the waveform F1 is obtained by overlapping the suction pulsation Fo6 caused by fluid leakage on the antiphase pulsation G1. Hereinafter, the suction pulsation shown by the waveform F1 is referred to as a suction pulsation F1. Since the valleys of the antiphase pulsation G1 generated due to the existence of the non-twisted portions 240, 250 are in the vicinity of the rotational angle θ=30°×(2n−1), the upper limit of the peaks of the suction pulsation F1 is suppressed. Here, n is an integer greater than or equal to one.

The first embodiment has the following advantages.

(1) The combination of the non-twisted portions 240, 250 and the twisted portions 241, 242, 251, 252 cause the volumetric change in the suction space S to periodically fluctuate. The valleys of the antiphase pulsation G1 generated by the fluctuation of the volumetric change in the suction space S match the peaks of the suction pulsation Fo6 caused by fluid leakage. Thus, the degree of the suction pulsation F1 (the difference A1 between the maximum amplitude and the minimum amplitude of the suction pulsation F1 shown in FIG. 3B) is reduced compared to the degree of the suction pulsation Fo6 caused by fluid leakage (the difference Ao between the maximum amplitude and the minimum amplitude of the suction pulsation Fo6 caused by fluid leakage shown in FIG. 3B). That is, the suction pulsation caused by fluid leakage is reduced by selecting an optimum phase of the fluctuation of the volumetric change in the suction space S by combining the non-twisted portions 240, 250 and the twisted portions 241, 242, 251, 252.

(2) Increasing the length L of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 (shown in FIGS. 1B, 1C, and 3A) increases the fluctuation of the volumetric change in the suction space S, and reducing the length L of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 reduces the fluctuation of the volumetric change in the suction space S. Setting the length L of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 in an appropriate manner further reduces the suction pulsation caused by fluid leakage.

(3) Changing the arrangement position of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 changes the position of the valleys of the antiphase pulsation G1 relative to the rotational angle θ. Setting the position of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 in an appropriate manner further reduces the suction pulsation caused by fluid leakage.

As described above, by changing the setting position of the different shape variation portions (non-twisted portion 240) in the axial direction of the rotation axes 151, 181 of the rotors and changing the range of the different shape variation portions in the axial direction of the rotation axes 151, 181, the phase of the pulsation generated by the fluctuation of the volumetric change in the suction space S is changed. By matching the valleys of the phase of the pulsation generated by the fluctuation of the volumetric change with the peaks of the suction pulsation caused by the fluid leakage, the suction pulsation caused by the fluid leakage is reduced. That is, the suction pulsation caused by fluid leakage is reduced by setting the phase of the suction pulsation caused by the fluctuation of the volumetric change such that the waveform of the suction pulsation generated by the fluctuation of the volumetric change caused by providing the different shape variation portions and the waveform of the suction pulsation caused by fluid leakage cancel each other to be reduced. That is, if an optimum phase of the pulsation, which is caused by the fluctuation of the volumetric change in the suction space S, is selected by combining the different shape variation portions and the twisted portions, the suction pulsation caused by fluid leakage is reduced.

(4) The periodical fluctuation of the volumetric change in the suction space S is preferably great in a range where the rotational angle θ is narrow. The non-twisted portions 240, 250, which are the different shape variation portions having a straight line form, are optimal in increasing the periodical fluctuation of the volumetric change in the suction space S in a range where the rotational angle θ is narrow.

(5) The configuration in which the non-twisted portions 240, 250 are located at the positions overlapping the center of the rotors 21, 22 in the axial direction of the rotation axes 151, 181 is convenient in matching the valleys of the antiphase pulsation G1 generated by the fluctuation of the volumetric change in the suction space S with the peaks of the suction pulsation Fo6 caused by fluid leakage.

A second embodiment will now be described with reference to FIGS. 4A to 5. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment.

As shown in FIG. 4A, teeth 24A of a rotor 21A have a loosely twisted portion 244 between the first twisted portion 241 and the second twisted portion 242. As shown in FIG. 4B, teeth 25A of a rotor 22A have a loosely twisted portion 254 between the first twisted portion 251 and the second twisted portion 252. A straight segment E10 a in the graph of FIG. 5 represents the twist angle variation of the loosely twisted portion 244, and a straight segment E20 a represents the twist angle variation of the loosely twisted portion 254. The loosely twisted portion 244 has the twist angle Φ about the rotation axis 151 which monotonically (in this case, linearly) changes with respect to the change in the position H in the axial direction of the rotation axis 151. The loosely twisted portion 254 has the twist angle Φ about the rotation axis 181 which changes monotonically (in this case, linearly) with respect to the change in the position H in the axial direction of the rotation axis 181. The loosely twisted portions 244, 254 are different shape variation portions having a variation in a twist angle smaller than the twist angle variations of the first twisted portions 241, 251 and the second twisted portions 242, 252.

When the length of the non-twisted portions 240, 250 in the axial direction of the rotation axes 151, 181 according to the first embodiment is equal to the length of the loosely twisted portions 244, 254 in the axial direction of the rotation axes 151, 181, the degree of the fluctuation of the volumetric change in the suction space S is smaller in the second embodiment than in the first embodiment. However, in the second embodiment also, the antiphase pulsation similar to the antiphase pulsation G1 of the first embodiment is obtained, and the suction pulsation caused by fluid leakage is reduced.

A third embodiment will now be described with reference to FIGS. 6A to 7. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment.

As shown in FIG. 6A, a rotor 21B is configured by laminating flat plates 31 in the axial direction of the rotation axis 151, and a non-twisted portion 240B of the rotor 21B is configured by laminating the flat plates 31 (four in the third embodiment). Similarly, as shown in FIG. 6B, a rotor 22B is configured by laminating flat plates 32 in the axial direction of the rotation axis 181, and a non-twisted portion 250B of the rotor 22B is configured by laminating the flat plates 32 (four in the third embodiment). The flat plates 31, 32 have the same shape and the same size, and the length of the non-twisted portions 240B, 250B in the axial direction of the rotation axes 151, 181 is greater than the thickness of the flat plates 31, 32.

The third embodiment also has the same advantages as the first embodiment. Furthermore, in the third embodiment, first twisted portions 241B, 251B and second twisted portions 242B, 252B are easily formed by laminating the flat plates 31, 32 in a twisted state, and the non-twisted portions 240B, 250B are also easily formed by laminating the flat plates 31, 32.

A fourth embodiment will now be described with reference to FIGS. 8 to 9. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment.

As shown in FIG. 8A, teeth 24C of a rotor 21C each have a nonlinear twisted portion 245 between a first twisted portion 241 and a second twisted portion 242. The twist angle Φ of the nonlinear twisted portion 245 changes with respect to the variation of the position in the axial direction of the rotation axis 151 in a manner represented by a nonlinear function (for example, quadratic function). As shown in FIG. 8B, teeth 25C of a rotor 22C each have a nonlinear twisted portion 255 between a first twisted portion 251 and a second twisted portion 252. The twist angle Φ of the nonlinear twisted portion 255 changes with respect to the variation of the position in the axial direction of the rotation axis 181 in a manner represented by a nonlinear function (for example, quadratic function). A curved segment E10 c in the graph of FIG. 9 represents the twist angle variation of the nonlinear twisted portion 245, and a curved segment E20 c represents the twist angle variation of the nonlinear twisted portion 255. The nonlinear twisted portions 245, 255 have different shape variation portions 245 r, 255 r, respectively. The different shape variation portions 245 r, 255 r have a smaller twist angle variation than the twist angle variations of the first twisted portions 241, 251 and the second twisted portions 242, 252.

The fourth embodiment provides an antiphase pulsation represented by a waveform, in which the peaks and the valleys of the antiphase pulsation G1 in FIG. 3C in a bent form is turned into a curved line. With such an antiphase pulsation also, the suction pulsation caused by fluid leakage is reduced. That is, the different shape variation portions (255) the twist angle Φ of which changes in a manner represented by a nonlinear function reduce the suction pulsation caused by fluid leakage.

A fifth embodiment will now be described with reference to FIGS. 10A to 11C. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment.

As shown in FIG. 10A, teeth 24D of a rotor 21D each include a helically twisted first twisted portion 241D, a helically twisted second twisted portion 242D, and a helically twisted third twisted portion 243. Furthermore, each tooth 24D includes a non-twisted portion 246, which is located between the first twisted portion 241D and the second twisted portion 242D, and a non-twisted portion 247, which is located between the second twisted portion 242D and the third twisted portion 243.

As shown in FIG. 10B, teeth 25D of a rotor 22D each include a helically twisted first twisted portion 251D, a helically twisted second twisted portion 252D, and a helically twisted third twisted portion 253. Furthermore, each tooth 25D includes a non-twisted portion 256, which is located between the first twisted portion 251D and the second twisted portion 252D, and a non-twisted portion 257, which is located between the second twisted portion 252D and the third twisted portion 253.

A straight segment E31 of a variation line E3 in the graph of FIG. 11A represents the twist angle variation of the first twisted portion 241D, a straight segment E32 of the variation line E3 represents the twist angle variation of the second twisted portion 242D, and a straight segment E33 of the variation line E3 represents the twist angle variation of the third twisted portion 243. A straight segment E34 of the variation line E3 represents the twist angle variation of the non-twisted portion 246, and a straight segment E35 of the variation line E3 represents the twist angle variation of the non-twisted portion 247.

A straight segment E41 of a variation line E4 in the graph of FIG. 11A represents the twist angle variation of the first twisted portion 251D, a straight segment E42 of the variation line E4 represents the twist angle variation of the second twisted portion 252D, a straight segment E43 of the variation line E4 represents the twist angle variation of the third twisted portion 253. A straight segment E44 of the variation line E4 represents the twist angle variation of the non-twisted portion 256, and a straight segment E45 of the variation line E4 represents the twist angle variation of the non-twisted portion 257.

The non-twisted portion 246 is located between the position corresponding to the twist angle Φ=15° of the first twisted portion 241D and the position corresponding to the twist angle Φ=15° of the second twisted portion 242D, and the non-twisted portion 247 is located between the position corresponding to the twist angle Φ=45° of the second twisted portion 242D and the position corresponding to the twist angle Φ=45° of the third twisted portion 243. That is, the non-twisted portion 246 is located at a position midway between the center of the rotor 21D in the axial direction of the rotation axis 151 and one end of the rotor 21D (the end surface 211), and the non-twisted portion 247 is located at a position midway between the center of the rotor 21D in the axial direction of the rotation axis 151 and the other end of the rotor 21D (the end surface 212).

The non-twisted portion 256 is located between the position corresponding to the twist angle Φ=−15° of the first twisted portion 251D and the position corresponding to the twist angle Φ=−15° of the second twisted portion 252D, and the non-twisted portion 257 is located between the position corresponding to the twist angle Φ=−45° of the second twisted portion 252D and the position corresponding to the twist angle Φ=−45° of the third twisted portion 253. That is, the non-twisted portion 256 is located at a position midway between the center of the rotor 22D in the axial direction of the rotation axis 181 and one end of the rotor 22D (the end surface 221), and the non-twisted portion 257 is located at a position midway between the center of the rotor 22D in the axial direction of the rotation axis 181 and the other end of the rotor 22D (the end surface 222).

A waveform G2 in FIG. 11C represents the pulsation generated by the fluctuation of the volumetric change in the suction space S. In the case with the rotors 21D, 22D, the volumetric change in the suction space S fluctuates due to the existence of the non-twisted portions 246, 247, 256, 257. The valleys of the pulsation shown by the waveform G2 are in the vicinity of the rotational angle θ=15°×(2n−1). Here, n is an integer greater than or equal to one. Hereinafter, the pulsation represented by the waveform G2 is referred to as an antiphase pulsation G2.

A waveform Fo12 in FIG. 11B shows one example of the order component that is double the fundamental order of the suction pulsation caused by fluid leakage when rotors without the non-twisted portions 246, 247, 256, 257 are used. In the case of the roots pump that uses the rotors with three teeth, the double of the fundamental order of the suction pulsation caused by fluid leakage is 12th order. Hereinafter, the suction pulsation of the 12th order component shown by the waveform Fo12 is referred to as a 12th order component pulsation Fo12 caused by fluid leakage. The peaks of the 12th order component pulsation Fo12 caused by fluid leakage are in the vicinity of the rotational angle θ=15°×(2n−1), and the valleys of the 12th order component pulsation Fo12 caused by fluid leakage are in the vicinity of the rotational angle θ=15°×2n. Here, n is an integer greater than or equal to one.

The waveform F2 in FIG. 11B shows one example of the suction pulsation when the rotor 21D having the non-twisted portions 246, 247 and the rotor 22D having the non-twisted portions 256, 257 are used. The suction pulsation shown by the waveform F2 is obtained by overlapping the 12th order component pulsation Fo12 caused by fluid leakage on the antiphase pulsation G2. Hereinafter, the suction pulsation shown by the waveform F2 is referred to as a suction pulsation F2. Since the valleys of the antiphase pulsation G2 generated due to the existence of the non-twisted portions 246, 247, 256, 257 are in the vicinity of the rotational angle θ=15°×(2n−1), the upper limit of the peaks of the suction pulsation F2 is suppressed. Here, n is an integer greater than or equal to one.

The fifth embodiment is advantageous in reducing the suction pulsation component of the order that is double the fundamental order.

A sixth embodiment will now be described with reference to FIGS. 12A to 13C. Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the first embodiment.

As shown in FIG. 12A, a rotor 33 includes two teeth 35, which protrude in the radial direction of the rotary shaft 15, and a rotor 34 includes two teeth 36, which protrude in the radial direction of the rotary shaft 18. The two teeth 35 of the rotor 33 are located at equal angular intervals of 180° about the rotation axis 151 of the rotary shaft 15, and the rotor 33 has a rotational symmetry of 180° about the rotation axis 151. Similarly, the two teeth 36 of the rotor 34 are located at equal angular intervals of 180° about the rotation axis 181 of the rotary shaft 18, and the rotor 34 has a rotational symmetry of 180° about the rotation axis 181.

As shown in FIG. 12B, each tooth 35 includes a first twisted portion 351, which is helically twisted clockwise about the rotation axis of the rotor 33 (that is, the rotation axis 151 of the rotary shaft 15), a second twisted portion 352, which is helically twisted clockwise about the rotation axis 151, and a non-twisted portion 350, which is located between the first twisted portion 351 and the second twisted portion 352. The twist angle of the first twisted portion 351 and the second twisted portion 352 change linearly along the axial direction of the rotation axis 151. The non-twisted portion 350 has a straight line form parallel to the rotation axis 151 (that is, a form that does not twist along the axial direction of the rotation axis 151).

As shown in FIG. 12C, each tooth 36 includes a first twisted portion 361, which is helically twisted counterclockwise about the rotation axis of the rotor 34 (that is, the rotation axis 181 of the rotary shaft 18), a second twisted portion 362, which is helically twisted counterclockwise about the rotation axis 181, and a non-twisted portion 360, which is located between the first twisted portion 361 and the second twisted portion 362. The twist angle of the first twisted portion 361 and the second twisted portion 362 change linearly along the axial direction of the rotation axis 181. The non-twisted portion 360 has a straight line form parallel to the rotation axis 181 (that is, a form that does not twist along the axial direction of the rotation axis 181).

The first twisted portion 351 of the rotor 33 meshes with the first twisted portion 361 of the rotor 34, and the second twisted portion 352 of the rotor 33 meshes with the second twisted portion 362 of the rotor 34. The non-twisted portion 350 of the rotor 33 meshes with the non-twisted portion 360 of the rotor 34.

A variation line E7 in the graph of FIG. 13A represents the relationship between the twist angle Φ and the position H in the axial direction of the rotation axis 151 regarding parts of the rotor 33 where the lengths of the radial lines, which extend from the rotation axis 151 of the rotor 33 to the circumferential surfaces of the teeth 35, are equal (for example, the vertexes of the teeth 35 of the rotor 33). The position of an end surface 331 of the rotor 33 is represented by the position H=0, the position of an end surface 332 of the rotor 33 is represented by the position H=He. The twist angle corresponding to the position of the end surface 331 is represented by the twist angle Φ=0°, and the twist angle corresponding to the position of the end surface 332 is represented by the twist angle Φ=Φe. A straight segment E71 of the variation line E7 represents the twist angle variation of the first twisted portion 351, and a straight segment E72 of the variation line E7 represents the twist angle variation of the second twisted portion 352. A straight segment E70 of the variation line E7 represents the twist angle variation of the non-twisted portion 350.

A variation line E8 in the graph of FIG. 13A represents the relationship between the twist angle Φ and the position H in the axial direction of the rotation axis 181 regarding parts of the rotor 34 where the lengths of the radial lines, which extend from the rotation axis 181 of the rotor 34 to the circumferential surfaces of the teeth 36, are equal (for example, vertexes of the teeth 36 of the rotor 34). The position of an end surface 341 of the rotor 34 is represented by the position H=0, the position of an end surface 342 of the rotor 34 is represented by the position H=He. The twist angle corresponding to the position of the end surface 341 is represented by the twist angle Φ=0°, and the twist angle corresponding to the position of the end surface 342 is represented by the twist angle Φ=−Φe. A straight segment E81 of the variation line E8 represents the twist angle variation of the first twisted portion 361, and a straight segment E82 of the variation line E8 represents the twist angle variation of the second twisted portion 362. A straight segment E80 of the variation line E8 represents the twist angle variation of the non-twisted portion 360.

In the sixth embodiment, Φe=90°, and −Φe=−90°. Also, the straight segment E70 is at the position of Φ=45°, and the straight segment E80 is at the position of Φ=−45°. That is, the length of the first twisted portion 351 of the rotor 33 in the direction of the rotation axis 151 is equal to that of the second twisted portion 352. Furthermore, the non-twisted portion 350 is located between the position corresponding to the twist angle Φ=45° of the first twisted portion 351 and the position corresponding to the twist angle Φ=45° of the second twisted portion 352, and the non-twisted portion 350 is located at a position overlapping the center of the rotor 33 in the direction of the rotation axis 151. Similarly, the length of the first twisted portion 361 of the rotor 34 in the direction of the rotation axis 181 is equal to that of the second twisted portion 362. Furthermore, the non-twisted portion 360 is located between the position corresponding to the twist angle Φ=−45° of the first twisted portion 361 and the position corresponding to the twist angle Φ=−45° of the second twisted portion 362, and the non-twisted portion 360 is located at a position overlapping the center of the rotor 34 in the direction of the rotation axis 181.

A waveform G3 in FIG. 13C represents the pulsation generated by the fluctuation of the volumetric change in the suction space S. In the case where the rotors 33, 34 are used, the volumetric change in the suction space S fluctuates due to the existence of the non-twisted portions 350, 360. The valleys of the pulsation shown by the waveform G3 are in the vicinity of the rotational angle θ=45°×(2n−1). Here, n is an integer greater than or equal to one. Hereinafter, the pulsation shown by the waveform G3 is referred to as an antiphase pulsation G3.

A waveform Fo4 in FIG. 13B shows one example of the suction pulsation caused by fluid leakage in a case where rotors without the non-twisted portions 350, 360 are used. In the case of the roots pump which uses the rotors with two teeth, the fundamental order of the suction pulsation caused by fluid leakage is fourth order. Hereinafter, the suction pulsation shown by the waveform Fo4 is referred to as a suction pulsation Fo4 caused by fluid leakage. The valleys of the suction pulsation Fo4 caused by fluid leakage are in the vicinity of the rotational angle θ=45°×(2n−1), and the peaks of the suction pulsation Fo4 caused by fluid leakage are in the vicinity of the rotational angle θ=45°×2n. Here, n is an integer greater than or equal to one.

A waveform F3 in FIG. 13B shows one example of the suction pulsation when the rotors 33, 34 including the non-twisted portions 350, 360 are used. The suction pulsation shown by the waveform F3 is obtained by overlapping the suction pulsation Fo4 caused by fluid leakage on the antiphase pulsation G3. Hereinafter, the suction pulsation shown by the waveform F3 is referred to as a suction pulsation F3. Since the valleys of the antiphase pulsation G3 generated due to the existence of the non-twisted portions 350, 360 are in the vicinity of the rotational angle θ=415°×(2n−1), the upper limit of the peaks of the suction pulsation F3 is suppressed. Here, n is an integer greater than or equal to one.

The present invention may also be embodied in the following forms.

A pair of rotors (rotors having three teeth) represented by variation lines E13, E14 shown in FIG. 14 may be used. Straight segments E130, E140 of the variation lines E13, E14 correspond to the straight segments E10, E20 of FIG. 3A, and curved segments E131, E132, E141, E142 represent the twist angle variation of the twisted portions the twist angle of which monotonically (in this case, nonlinearly) changes. Changing monotonically means that the twist angle varies in a manner represented by a monotonically increasing function or a monotonically decreasing function.

A pair of rotors (rotors having three teeth) represented by variation lines E15, E16 shown in FIG. 15 may be used. Straight segments E150, E160 of the variation lines E15, E16 correspond to the straight segments E10, E20 of FIG. 3A, and curved segments E151, E152, E161, E162 represent the twist angle variation of the twisted portions the twist angle of which monotonically (in this case, nonlinearly) changes.

A pair of rotors (rotor having three teeth) represented by variation lines E17, E18 shown in FIG. 16 may be used. Curved segments E170, E180 of the variation lines E17, E18 correspond to the curved segments E10 c, E20 c of FIG. 9, and straight segments E171, E172, E181, E182 represent the twist angle variation of the twisted portions the twist angle of which monotonically (in this case, linearly) change.

According to the first to fifth embodiments, and embodiments illustrated in FIGS. 14, 15, and 16, the rotors including three teeth are used, and the twist angle Φ is set to 60°. In such a case where the rotors including three teeth are used, the twist angle Φ may be greater than 60°, and may be an integral multiple of 60°.

In the case where the rotors including three teeth are used, it is optimal that the twist angle Φ satisfies the equation (1) when 3 is substituted for n. However, the present invention may be applied even when the twist angle Φ does not satisfy the equation (1).

In the sixth embodiment, the rotors including two teeth are used, and the twist angle Φ is set to 90°. In such a case where the rotors including two teeth are used, the twist angle Φ may be greater than 90°, and may be an integral multiple of 90°.

In the case when the rotors including two teeth are used, it is optimal that the twist angle Φ satisfies the equation (1) when 2 is substituted for n. However, the present invention may be applied even when the twist angle Φ does not satisfy the equation (1).

The present invention may be applied to rotors including four or more teeth.

The rotors 33, 34 according to the sixth embodiment may be configured by laminating flat plates.

The present invention may be applied to a serial or parallel roots-type fluid machine, in which a set of rotors (the set of rotors 21, 22 according to the first embodiment) accommodated in the pump chamber 231, which communicates with the inlet 281, and at least one pump chamber different from the pump chamber 231 are arranged next to one another in the axial direction of the rotation axis.

The present invention may be applied to a roots-type fluid machine in which a set of three or more rotors are accommodated in the rotor housing. 

1. A roots-type fluid machine comprising a set of rotors and a rotor housing, which accommodates the rotors and has a suction space, the set of rotors meshing with each other and rotate in the rotor housing so that fluid is drawn into the suction space and discharged from the rotor housing, wherein each of the set of rotors includes a tooth having a twisted portion and a different shape variation portion, the twisted portion having a twist angle that changes linearly or non-linearly about a rotation axis of the corresponding rotor with respect to a variation of the position in the direction of the axis, and the different shape variation portion having a twisted angle that changes by a smaller degree than the variation of the twist angle of the twisted portion.
 2. The fluid machine according to claim 1, wherein the twisted potion is helical and the different shape variation portion has a straight line form parallel to the rotation axis.
 3. The fluid machine according to claim 1, wherein the twisted potion is helical and the different shape variation portion has a form the twist angle of which changes with respect to the variation of the position in the axial direction of the rotation axis in a manner represented by a nonlinear function.
 4. The fluid machine according to claim 1, wherein the different shape variation portion is provided at a position including the center of the rotor in the direction of the rotation axis.
 5. The fluid machine according to claim 4, wherein the twisted portion is provided on each side of the different shape variation portion in the direction of the rotation axis, and the lengths of the twisted portions are equal.
 6. The fluid machine according to claim 1, wherein the different shape variation portion is provided at a position including midway between the center of the rotor in the direction of the rotation axis and each of the ends of the associated rotor.
 7. The fluid machine according to claim 1, wherein each rotor is configured by laminating a plurality of flat plates having the same shape and the same size in the direction of the rotation axis, and the length of the different shape variation portion in the direction of the rotation axis is greater than the thickness of each flat plate.
 8. The fluid machine according to claim 1, wherein, in each rotor, the length of the different shape variation portion in the direction of the rotation axis is shorter than the length of the twisted portion in the direction of the rotation axis. 